day21

day21p1/solution.go

@@ -0,0 +1,194 @@
+package day21p1
+
+import (
+	"fmt"
+	"io"
+	"sort"
+	"strconv"
+	"strings"
+
+	"aoc/utils"
+)
+
+type Keypad map[rune]utils.Point
+
+func (k Keypad) String() string {
+	runes := make([]rune, 0, len(k))
+	for r := range k {
+		runes = append(runes, r)
+	}
+	sort.Slice(runes, func(i, j int) bool {
+		return runes[i] < runes[j]
+	})
+	return string(runes)
+}
+
+var numKeypad = Keypad{
+	'7': {X: 0, Y: 0},
+	'8': {X: 1, Y: 0},
+	'9': {X: 2, Y: 0},
+	'4': {X: 0, Y: 1},
+	'5': {X: 1, Y: 1},
+	'6': {X: 2, Y: 1},
+	'1': {X: 0, Y: 2},
+	'2': {X: 1, Y: 2},
+	'3': {X: 2, Y: 2},
+	'X': {X: 0, Y: 3},
+	'0': {X: 1, Y: 3},
+	'A': {X: 2, Y: 3},
+}
+
+var dirKeypad = Keypad{
+	'X': {X: 0, Y: 0},
+	'^': {X: 1, Y: 0},
+	'A': {X: 2, Y: 0},
+	'<': {X: 0, Y: 1},
+	'v': {X: 1, Y: 1},
+	'>': {X: 2, Y: 1},
+}
+
+func writeVerticalFirst(dx, dy int) string {
+	sb := &strings.Builder{}
+	for dy < 0 {
+		sb.WriteRune('^')
+		dy++
+	}
+	for dy > 0 {
+		sb.WriteRune('v')
+		dy--
+	}
+	for dx < 0 {
+		sb.WriteRune('<')
+		dx++
+	}
+	for dx > 0 {
+		sb.WriteRune('>')
+		dx--
+	}
+	sb.WriteRune('A')
+	return sb.String()
+}
+
+func writeHorizontalFirst(dx, dy int) string {
+	sb := &strings.Builder{}
+	for dx < 0 {
+		sb.WriteRune('<')
+		dx++
+	}
+	for dx > 0 {
+		sb.WriteRune('>')
+		dx--
+	}
+	for dy < 0 {
+		sb.WriteRune('^')
+		dy++
+	}
+	for dy > 0 {
+		sb.WriteRune('v')
+		dy--
+	}
+	sb.WriteRune('A')
+	return sb.String()
+}
+
+func getMoves(dx, dy int) []string {
+	moves := []string{writeVerticalFirst(dx, dy)}
+	if dx != 0 && dy != 0 {
+		moves = append(moves, writeHorizontalFirst(dx, dy))
+	}
+	return moves
+}
+
+func doesMoveOverEmpty(point utils.Point, move string, keypad Keypad) bool {
+	for _, r := range move {
+		switch r {
+		case '^':
+			point.Y--
+		case 'v':
+			point.Y++
+		case '<':
+			point.X--
+		case '>':
+			point.X++
+		}
+		if keypad['X'] == point {
+			return true
+		}
+	}
+	return false
+}
+
+type MemoizedKey struct {
+	input   string
+	keypads int
+}
+
+type MemoizedValue struct {
+	length int
+	ok     bool
+}
+
+var memoized map[MemoizedKey]MemoizedValue
+
+func dfs(input string, keypads []Keypad) (int, bool) {
+	key := MemoizedKey{input: input, keypads: len(keypads)}
+	if value, ok := memoized[key]; ok {
+		return value.length, value.ok
+	}
+	point := keypads[0]['A']
+	length := 0
+	for _, r := range input {
+		newPoint := keypads[0][r]
+		dx := newPoint.X - point.X
+		dy := newPoint.Y - point.Y
+		moves := getMoves(dx, dy)
+		shortest := -1
+		found := false
+		for _, move := range moves {
+			if doesMoveOverEmpty(point, move, keypads[0]) {
+				continue
+			}
+			if len(keypads) == 1 {
+				shortest = len(move)
+				found = true
+				break
+			}
+			if candidate, ok := dfs(move, keypads[1:]); ok {
+				if !found || candidate < shortest {
+					shortest = candidate
+					found = true
+				}
+			}
+		}
+		if !found {
+			memoized[key] = MemoizedValue{length: 0, ok: false}
+			return 0, false
+		}
+		length += shortest
+		point = newPoint
+	}
+	memoized[key] = MemoizedValue{length: length, ok: true}
+	return length, true
+}
+
+func getSum(input []string) int {
+	memoized = make(map[MemoizedKey]MemoizedValue)
+	keypads := []Keypad{numKeypad, dirKeypad, dirKeypad}
+	sum := 0
+	for _, line := range input {
+		length, ok := dfs(line, keypads)
+		if !ok {
+			fmt.Println("No path found for", line)
+			return -1
+		}
+		num, _ := strconv.Atoi(line[:len(line)-1])
+		sum += length * num
+	}
+	return sum
+}
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+
+	return getSum(lines)
+}

day21p1/solution_test.go

@@ -0,0 +1,37 @@
+package day21p1
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `029A
+980A
+179A
+456A
+379A`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer int
+	}{
+		{testInput, 126384},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(int)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}